Scripts and executables must do two things (at minimum) in order to function as Alignak plugins:

Exit with one of several possible return values

Print at least one line of text output to the standard stdout

Alignak do not matter about the inner workings of a plugin. Only the interface between Alignak and the plugin is of any concern.

If you are interested in having a plugin that is very performant to use with Alignak, you should consider making it an Alignak Worker or Module and it will be daemonized by the Alignak poller or receiver daemon. You can look at the existing modules…

Alignak determines the status of an host or service by evaluating the return code from its check plugin.
The following table shows a list of valid return codes, along with their corresponding service or host states.

Plugin Return Code

Service State

Host State

0

OK

UP

1

WARNING

DOWN/UNREACHABLE*

2

CRITICAL

DOWN/UNREACHABLE

3

UNKNOWN

DOWN/UNREACHABLE

The process by which Alignak determines whether or not a host is DOWN or UNREACHABLE is discussed here.

At minimum, plugins should return at least one of text output. Plugins can optionally return multiple lines of output. Plugins may also return optional performance data that can be processed by external applications. The basic format for plugin output is shown below:

Assume we have a plugin that returns one line of output that looks like this:

DISKOK-freespace:/3326MB(56%);

If this plugin was used to perform a service check, the entire line of output will be stored in the $SERVICEOUTPUT$ macro.

Case 2: One line of output (text and perfdata)

A plugin can return optional performance data for use by external applications. To do this, the performance data must be separated from the text output with a pipe (|) symbol like such as:

DISKOK-freespace:/3326MB(56%)|/=2643MB;5948;5958;0;5968

If this plugin was used to perform a service check, the left part of the output (before the pipe separator) will be stored in the $SERVICEOUTPUT$ macro and the right part of the output (after the pipe separator) will be stored in the $SERVICEPERFDATA$ macro.

Case 3: Multiple lines of output (text and perfdata)

A plugin may optionally return multiple lines of both text output and perfdata, like such as:

If this plugin was used to perform a service check, the left part of the first line of output (before the pipe separator) will be stored in the $SERVICEOUTPUT$ macro. The right part of the first line and the subsequent lines are concatenated (with spaces) and stored in the $SERVICEPERFDATA$ macro. The blue portions of the 2nd _ 5th lines of output will be concatenated (with escaped newlines) and stored in $LONGSERVICEOUTPUT$ the macro.

Alignak will only read the first 8 KB of data that a plugin returns. This is done in order to prevent runaway plugins from dumping megs or gigs of data back to Alignak. This 8 KB output limit is easy to change if you need. Simply edit the value of the max_plugins_output_length variable in the configuration file.